Fluid-cooled airfoil

ABSTRACT

An improved fluid-cooled airfoil having spaced leading and trailing edge chambers and a serpentine passage therebetween. Coolant is delivered to the leading and trailing edge chambers, respectively, by an impingement insert and the portion of the serpentine chamber adjacent the trailing edge chamber. Various features, such as turbulence promoters, inclined trailing edge passages and film-cooling passageways, are provided to enhance the heat-transfer properties of the airfoil.

United States Patent 1111 3,628,885

[72] in en Sidensljck, James E.; 3,369,792 2/1968 Kraimer et al. 4 l 5/]l5 Richard W. Brown; Herbert E. Nichols; 3,370,829 2/1968 Banthin etal..... 4 1 SH Frederick Burggrai, all of Cincinnati, Ohio 3,388,888 6/l 968 Kercher et al. 4 I 5/] i5 [21] Appdl. N 3 31 2969 3,528,75] 9/1970Quinones et al. 4 l 5/! i5 [22] Fi e ct.

[] Patented ml 1 1 185 541 2/1 955 :2532 PATENTS 416/97 I [73] Ass'gneeElem" 985,772 3/1965 Great Britain 416 96 Primary Examiner- Everette A.Powell, .I r. Attorneys-Derek P. Lawrence. Erwin F. Berrier, Jr., Lee H.Sachs, Frank L. Neuhauser, Oscar B. Waddell and Joseph [54] FLUID-COOLEDAlRFOlL 11 Claims, 5 Drawing Figs.

521 u.s.c| 416/97 m 511 1111.0 F0-ld5/08 FieldoiSearch ..-....4l6/95-97,

. ABSTRACT: An improved fluid-cooled airfoil having spaced90,9l,92,4l5/ll5 leading and trailing edge chambers and a serpentmepassage [56] References Cited therebetween. Coolant is delivered to theleading and trailing UNITED STATES PATENTS edge chambers, respectively,by an impingement insert and the portion of the serpentine chamberadjacent the trailing 521:2 edge chamber. Various features, such asturbulence 3/1965 AS 416/97) promoters, inclined trailing edge passagesand film-cooling 3220697 11/1965 smfilland 'i'' 416/96 passageways, areprovided to enhance the heat-transfer pro- 3,301,526 1/1967 Chamberlain:415/115 peniesoftheairm" FLUID-COOLED AIRFOIL This invention relates toturbomachinery and, more particularly, to an improved fluid-cooledairfoil such as a turbine blade for use therein. The invention hereindescribed was made in the course of or under a contract, or asubcontract thereunder, with the United States Department of the AirForce.

It is well known that the efficiency of a gas turbine engine is relatedto the operating temperature of the turbine and that engine efflciencymay be increased, in theory, by increasing the operating temperature. Asa practical matter, however, the maximum turbine-operating temperatureis generally limited by the high-temperature capabilities of the variousturbine elements, with the turbine blades or vanes usually being themost limiting of such elements.

To extend the upper operating temperature of the turbine and, hence,make available some of the theoretical efficiency increase, variousdesigns for cooling airfoils such as turbine blades or vanes usingrelatively cool air discharged or extracted from the compressor havebeen devised. One such arrangement is shown in copending applicationSer. No. 533,l filed Feb. 26, 1966, and assigned to the assignee of thisapplication now U.S. Pat. No. 3,533,711 issued Oct. l3,

With such arrangements, however, since the use of compressor pressurizedair represents a charge against or is in and of itself subtractive fromengine efficiency, it is important that the heat-transfer properties ofthe blade be such as to minimize the amount of coolant required tomaintain the blade at a satisfactory operating temperature.

Certain efficiency losses in a gas turbine engine usually occur as aresult of motive fluid leakage between the turbine blade and cooperatingturbine shroud. By effluxing turbine blade cooling air through the outerradial end of the blade it has been found that such leakage may bereduced or eliminated. Accordingly, in terms of overall effectiveness,it is important that the cooling design be such as to allow sufficientdischarge of cooling air through the blade tip to effectively block tipleakage.

A primary object of this invention is to provide a fluidcooled airfoilhaving improved cooling heat-transfer characteristics.

Another object of this invention is to provide an improved turbine bladeof the type adapted to receive compressor pressurized air for coolingpurposes.

A further object of this invention is to provide a turbine bladestructure, as above, wherein a sufficient portion of the cooling fluidor media may be discharged through the blade tip so as to reduce motivefluid tip leakage.

Yet another object of this invention is a turbomachinery airfoil adaptedto efficiently utilize a coolant fluid to achieve reduced peak metaltemperatures and thermal gradients.

Briefly stated, the above and other objects which will become apparentupon reading the following description of the preferred embodiment areachieved in the present invention by providing an airfoil having spacedleading and trailing edge chambers and at least one intermediateserpentine passage in flow communication with a source of coolantthrough that portion of the passage most closely adjacent the trailingedge chamber. Means are provided to receive coolant and impinge itagainst the leading edge chamber wallto provide a high heat-transferrate in that sector of the blade. The airfoil may include film-coolingpassages formed through one or both sidewalls and communicating with theleading edge chamber to provide a film of coolant along the exteriorsurface of the sidewalls. The serpentine passage preferably includesmeans for promoting turbulence in the coolant boundary layer to enhancethe heat transfer in the midchord region of the airfoil. Coolant isdelivered to the trailing edge chamber through the adjacent serpentinepassage portion. In the form of a turbine blade, the airfoil ispreferably defined by a hollow cast member having attachment and airfoilportions intermediate an open inner and an outer end. The outer end ofthe cast member is closed by a perforated tip cap which in part definesand provides an efflux path for the chambers and serpentine passage.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of this invention, it isbelieved that the invention will be better understood upon reading thefollowing description of the preferred embodiment in connection with theaccompanying drawings wherein:

FIG. 1 is a partial perspective view of a turbine rotor employing theimproved fluid-cooled airfoil of this invention, with said airfoiltaking the form of a turbine blade;

FIG. 2 is a side elevational view, drawn in partial section and to anenlarged scale, of the turbine blade of FIG. I;

FIG. 3 is an enlarged cross-sectional view taken along lines 3-3 of FIG.2;

FIG. 4 is a partial perspective sectional view of the airfoil portion ofthe turbine blade of FIG. 1; and

FIG. 5 is a graph showing the improvement in convective heat-transfercoefficient in the midchord region of the turbine blade of FIG. I.

Like reference numerals will be used in referring to like partsthroughout the following description of the preferred embodiment.

With reference now to FIG. vl, the improved airfoil of this inventionhas been shown in the form of a turbine blade at 10 as comprising anairfoil portion 12 and an attachment or root portion 14 adapted tosecure the blade to a turbine rotor 16 in a well-known manner with theairfoil portion 12 extending generally radially across a motive fluidflow passage 18. The airfoil portion 12 includes a leading edge 20 and achordwise spaced trailing edge 22 which are interconnected by convex andconcave sidewalls 24 and 26, respectively. The airfoil portion 12 issuitably shaped in a well-known manner so as to efficiently extractenergy from the motive fluid as it flows spanwise of the blade andimpart rotary motion to the rotor 16.

As best shown in FIG..2, the blade structure of this invention ispreferably formed as a hollow cast member 28 having an open inner end 30and an outer or distal end 32. The outer end 32 is closed by a tip cap34 which may be cast integrally with the member 28 or suitably securedthereto as by welding or brazing.

The root or attachment portion 14 is provided with means, preferablytaking the form of plenums or receiving chambers 35 and 36, forreceiving a flow of suitable cooling fluid through the open inner end30. A leading edge chamber 38 extends longitudinally of the airfoilportion 12 and is cooperatively formed by the cast member 28 and the tipcap 34. In order to provide efficient cooling for the leading edge 20,means designated generally at 40 are provided, in flow communicationwith the cooling fluid of chamber 35, for impinging the cooling fluidagainst at least the forwardmost portion of the leading edge chamberwall as a plurality of high-velocity jets. The impingement means 40preferably comprises a thinwall tubular insert 42 which projects intothe leading edge cavity or chamber 38 with its walls in close-spacedrelationship to the chamber walls. The insert 42 is provided with aclosed outer or distal end 44 and an open inner end 46 in flowcommunication with the cooling fluid receiving means 35 and engaged witha necked opening 48 formed in the cast member intermediate chambers 35and 38. The insert 42 is formed with a plurality of small openings orperforations 49 through which the cooling fluid is expanded and impingedagainst the chamber wall as a plurality of high-velocity fluid jets.

' While the coolant-receiving means has been shown as comprising twodiscrete chambers 35 and 36, it will be recognized that a single chambermay be used.

The insert 42 may be provided with a plurality of projections 50 adaptedto engage the leading edge chamber walls to establish proper spacingtherebetween. It will be recognized, however, that the projections maybe carried by the cast member 28 or other suitable spacing means may beemployed.

While the insert 42 is preferably secured to the cast member 28 bybrazing in the area of engagement between the inserts open end 46 andthe cast member necked opening 48 so as to provide sealing between thecoolant'receiving means 35 and the chamber 38, it will be appreciatedthat other attachment means may be employed either alone or inconjunction with a brazed joint. For example, the insert 42 may beprovided with a collar at its open end which abuts the inner end of thechamber .38 and the portion of open end 46 which extends through theneck opening 48 into chamber 35 may be flared outwardly into grippingengagement with the cast member.

When brazing is used to join or secure the insert to the cast member 28,the cast member is preferably formed with ports 52 which communicatewith the necked opening 48 so as to enable the use of one port for thesupply of braze material to the joint and the other port for inspectionof the brazed joint, it being understood that the presence of brazematerial in such other port would indicate that the braze material hasflowed through the joint properly.

To provide cooling to the trailing edge region of the blade, a trailingedge chamber 54, which extends longitudinally of the airfoil portion 12adjacent its trailing edge 22, is cooperatively formed by the hollowcast member 28 and the tip cap 34.

At least one serpentine coolant flow passage is provided in the midspanregion of the airfoil portion 12 or intermediate the leading andtrailing edge chambers 38 and 54 by a plurality of longitudinallyextending chambers 56, 58, serially connected by alternating outer andinner chordwise passages or openings 60 and 62, respectively. Theserpentine passage chamber 56, adjacent the trailing edge chamber 54, isopen at its inner end 64 so as to be in flow communication with thecoolant-receiving means or chamber 36.

Coolant is preferably delivered to the trailing edge chamber 54 fromchamber 56 by a plurality of longitudinally spaced, chordwise passages66 which are formed through the wall member separating these chambers.

A plurality of pin fins 68, formed integrally with and extending betweensidewalls 24, 26, may be provided to enhance the convective heattransfer in the trailing edge region of the blade. To provide furthercooling to the trailing edge region of the blade, as well as to providemeans for effluxing the coolant from the chamber 54 so as to ensure acontinuous flow therethrough, a plurality of trailing edge passages 70are formed through the trailing edge 22.

In order to minimize the number of trailing edge passages requiredwithout increasing the trailing edge metal temperature, the passages 70are preferably inclined at some angle X relative to the spanwise axis ofthe blade, as best shown in FIG. 4, so that the metal thickness Y orspacing between passages taken longitudinally of the blade may beincreased without in creasing the metal thickness 2 taken normal to theaxes of the passages 70. Since the heat-transfer path is generallynormal to the direction of coolant flow through each passage 70, by soinclining the passages the heat-transfer characteristics of the trailingedge may be maintained essentially constant while increasing thelongitudinal spacing of the passages and thereby reducing the overallnumber of such passages and coolant flow requirements.

To increase the convective heat-transfer coefficient between thesidewalls 24, 26 and coolant during flow of the latter through theserpentine passage, the sidewalls are preferably formed with a pluralityof turbulence promoters or longitudinally spaced chordwise extendingribs 72 which project into the chambers 56, .58 (FIGS. 3 and 4) and areadapted to disturb and promote turbulence in the adjacent coolantboundary layer. Referring to FIG. 5, wherein the ratio of theheat-transfer coefficient obtained using applicant's ribs 72 to theheat-transfer coefficient in a smooth-walled chamber has been shown as afunction of the rib projecting height e and the chamber width D betweensidewalls 24 and 26, it will be observed that the convectiveheat-transfer coefficient using ribs 72 having an e/D ratio greater thanapproximately 0.02 is substantially increased over that of a smooth wallconfiguration.

Although FIG. 5 indicates that large e/D ratios are desirable, it willbe understood that as dimension e increases, the effective flow areathrough the chamber 58 decreases and hence pressure losses and flowreductions may be observed. With these constraints in mind, it has beenfound advantageous to employ a nominal e/D ratio of between 0.06 and0.07 so that with normal manufacturing or casting tolerance variations,the e/D ratio will remain above 0.02 yet will not increase to a pointadversely affecting the flow or pressure characteristics within theserpentine passage.

The longitudinal width of each rib 12 is preferably approximately equalto the rib projecting height e, with the longitudinal spacing betweenribs being approximately 10 times the rib height e.

By using such turbulence promoters, sufficiently high heattransfer ratesmay be achieved with lower coolant velocities which, in turn, permit theuse of a larger serpentine passage cross section or flow area withoutincreasing coolant requirements. By increasing passage flow area, bladeweight is reduced and the thermal mass and thermal response of themidspan region of the blade may be more closely matched to that of theleading and trailing edges so as to reduce temperature gradients.

To provide additional cooling to the midspan region of the blade,film-cooling holes 74, communicating with the leading edge chamber 38,may be provided for delivery ofa film or in sulating blanket of coolantalong the external surface of the sidewalls. While the blade has beenshown in FIG. 4 as having one row of longitudinally spaced film-coolingholes through each sidewall, it should be understood that sucharrangement may be varied. For example, the film-cooling holes need notbe arranged in discrete rows and, in instances where sufficient coolingis provided to the midspan region by other means, film cooling of one orboth sidewalls may be eliminated.

As best shown in FIG. 2, the tip cap 34 is preferably formed with aplurality of apertures 76 through which the coolant may efflux fromchambers 38, 54, 56 and 58 to provide cooling to the distal end of theturbine blade as well as enhanced blade tip-to-shroud sealing.

The use, operation and function of the present invention are as follows:

Pressurized fluid at a reduced temperature relative to the temperatureof the motive fluid in passage 18 and derived from a suitable sourcesuch as the compressor of a gas turbine engine is delivered to the blade10 through its open inner end 30. From receiving chambers 35, 36, thecoolant is efficiently directed radially outwardly into the leading edgeinsert 42 and serpentine passage chamber 56. The tip cap apertures 76and film-cooling holes 74 are sized relative to the insert impingementapertures 49 such that a sufficient pressure differential is maintainedacross the insert so that the coolant leaves the insert throughapertures 49 as a plurality of relatively highvelocityjets which impingeagainst at least the forward portion of the leading edge chambersidewall for efficient cooling of that sector of the blade. The coolantfluid is then further utilized by effluxing same from the chamber 38through the film cooling holes 74 and the tip cap apertures 76 so as toprovide an insulating blanket or film of cooling fluid along theexternal surface of the blade sidewalls and for cooling of the tip ordistal end of the turbine blade.

A portion of the fluid within chamber 56 is delivered to the trailingedge chamber 54 with the remaining portion flowing through theserpentine passage and tip cap apertures 76 to the motive fluid passage18. The coolant is effluxed from the trailing edge chamber throughinclined trailing edge passageways 56 and tip cap apertures 76 toprovide cooling for those regions of the blade.

As previously noted, by inclining the trailing edge passages 70, thetrailing edge may be maintained at a low operating temperature witheither reduced trailing edge chamber flow or with a greater proportionof such flow being discharged through the tip cap 34. By effluxing alarger portion of the coolant through the tip cap 34, improved sealingis achieved between the blade tip and its associated shroud whichenhances turbine efficiency and, where the coolant is derived from a gasturbine compressor, offsets a portion of the efficiency loss chargeableto such deviation.

Since the leading and trailing edges of the blade are usually subjectedto the most severe temperature environment, by first directing thecoolant to the leading and trailing edge portions of the turbine blade10 and then to the midspan portion of the blade through the serpentinepassage and filmcooling holes 74, the present invention increasesheat-transfer effectiveness in the leading and trailing edge regions ofthe airfoil. At the same time, by using turbulence promoters 72, thethermal response of the midpsan region of the airfoil may be closelymatched with that of the leading and trailing edge regions so as tominimize temperature gradients.

While the present invention has been described in connection with and isparticularly applicable to turbine blades, it will be understood thatthe present invention is not limited thereto and may be effectivelyemployed in compressor blades as well as static airfoils such ascompressor or turbine vanes.

Accordingly, while a preferred embodiment has been depicted anddescribed, it will be understood that many modifications and variationsmay be made thereto without departing from the fundamental theme of theinvention.

What is claimed is:

1. In an airfoil of the type adapted to project into a flow ofrelatively high-temperature fluid and having chordwise spaced leadingand trailing edges interconnected by concave and convex sidewalls,improved cooling means comprising:

a leading edge chamber formed in and extending longitudinally of saidairfoil adjacent said leading edge, means disposed internally of saidleading edge chamber for receiving a flow of coolant at a reducedtemperature relative to said high-temperature fluid and impinging saidcoolant against at least the forward portion of said leading edgechamber wall as a plurality of high-velocity jets, a trailing edgechamber formed in and extending longitudinally of said airfoil adjacentsaid trailing edge, a plurality of passageways formed through saidtrailing edge and communicating with said trailing edge chamber forefflux of coolant therefrom and cooling of said trailing edge, and aplurality of serially connected, longitudinally extending chambersdefining at least one serpentine passage intermediate said leading andtrailing edge chambers, the serpentine passage chamber adjacent saidtrailing edge chamber adapted to receive a flow of coolant for saidserpentine passage and being in flow communication with said trailingedge chamber for delivery of coolant thereto.

2. The improvement of claim 1 further characterized by and including aplurality of film cooling passageways formed through at least onesidewall and communicating with said leading edge chamber for 'efflux ofcoolant therefrom and delivery of a film of coolant along the exteriorsurface of said sidewall.

3. The improvement of claim 1 further characterized by and includingmeans for promoting turbulence in the coolant boundary layer of saidserpentine passage, whereby the crosssectional flow area of saidserpentine passage may be increased to effect close matching of themidspan region thermal response to that of the leading and trailing edgeregions without increased coolant requirements.

4. The improvement of claim 1 further characterized in that saidtrailing edge passageways are inclined relative to the chordwise axis ofsaid airfoil whereby a satisfactory operating temperature may bemaintained in the trailing edge with formed as a turbomachinery bladeand includes an attachment portion and an airfoil portion intermediateand respectively agjacent inner and outer ends, said attachment portiona apted to secure said airfoil to a rotor and formed with a chambertherein for receiving coolant for delivery to said impingement means andsaid serpentine passage chamber adjacent said trailing edge chamber.

7. The improvement of claim 6 wherein said airfoil is formed with anecked opening intermediate said leasing edge chamber and saidattachment portion chamber, said impingement means comprising aperforated tubular insert having an open inner end engaged in saidnecked opening and a closed outer end, and ports formed through saidairfoil and communicating with said necked opening to facilitate formingand inspection of a brazed joint between said insert and said airfoil.

8. The improvement of claim 6 wherein said longitudinal chambers areformed, in part, by a tip cap closing the outer end of said airfoil,said tip cap being perforated for discharge of coolant from saidlongitudinal chambers.

9. A fluid-cooled blade structure comprising a hollow cast member havingairfoil and attachment portions intermediate open inner and outer radialends, a tip cap secured to said cast member and closing said outer openend, said airfoil portion defined by spaced leading and trailing edgesjoined by spaced concave and convex sidewalls, means formed internallyof said attachment portion for receiving a flow of coolant, a leadingedge chamber formed internally of said airfoil portion adjacent saidleading edge, said leading edge chamber closed at its outer end by saidtip cap, a thin-walled insert secured to said hollow cast member andprojecting into said leading edge chamber with its sidewalls in closespaced relationship to the walls of said chamber, said insert disposedin flow communication with said coolant-receiving means, the walls ofsaid insert being perforated so as to impinge coolant fluid from saidinsert chamber against said leading edge chamber wall, a trailing edgechamber formed internally of said airfoil portion adjacent said trailingedge and closed at its outer end by said tip cap, a serpentine passageformed internally of said airfoil portion, in cooperation with said tipcap, intermediate said leading and trailing edge chambers, with theportion of said serpentine passage adjacent said trailing edge chamberin flow communication with said coolant-receiving means, a plurality ofpassageways extending between said trailing edge chamber and saidadjacent serpentine passage portion for delivery of said coolant to saidtrailing edge chamber, said tip cap being perforated so as to permitefflux of said coolant from said chambers and said serpentine passagethrough the outer end of said blade structure, a plurality offilm-cooling passages formed through at least one said sidewall fordelivery of a film of coolant thereto from said leading edge chamber,and a plurality of passageways formed through said trailing edge forefflux of said coolant from said trailing edge chamber.

10. The fluid-cooled blade structure of claim 3 further characterized byand including a plurality of ribs projecting into said serpentinepassage from said sidewalls, with the ratio of rib projecting height tothe spacing of said sidewalls being at least about 0.02.

11. The fluid-cooled blade structure of claim 9 further characterized inthat said trailing edge passageways are inclined relative to thechordwise axis of said airfoil portion.

1. In an airfoil of the type adapted to project into a flow ofrelatively high-temperature fluid and having chordwise spaced leadingand trailing edges interconnected by concave and convex sidewalls,improved cooling means comprising: a leading edge chamber formed in andextending longitudinally of said airfoil adjaCent said leading edge,means disposed internally of said leading edge chamber for receiving aflow of coolant at a reduced temperature relative to saidhightemperature fluid and impinging said coolant against at least theforward portion of said leading edge chamber wall as a plurality ofhigh-velocity jets, a trailing edge chamber formed in and extendinglongitudinally of said airfoil adjacent said trailing edge, a pluralityof passageways formed through said trailing edge and communicating withsaid trailing edge chamber for efflux of coolant therefrom and coolingof said trailing edge, and a plurality of serially connected,longitudinally extending chambers defining at least one serpentinepassage intermediate said leading and trailing edge chambers, theserpentine passage chamber adjacent said trailing edge chamber adaptedto receive a flow of coolant for said serpentine passage and being inflow communication with said trailing edge chamber for delivery ofcoolant thereto.
 2. The improvement of claim 1 further characterized byand including a plurality of film cooling passageways formed through atleast one sidewall and communicating with said leading edge chamber forefflux of coolant therefrom and delivery of a film of coolant along theexterior surface of said sidewall.
 3. The improvement of claim 1 furthercharacterized by and including means for promoting turbulence in thecoolant boundary layer of said serpentine passage, whereby thecross-sectional flow area of said serpentine passage may be increased toeffect close matching of the midspan region thermal response to that ofthe leading and trailing edge regions without increased coolantrequirements.
 4. The improvement of claim 1 further characterized inthat said trailing edge passageways are inclined relative to thechordwise axis of said airfoil whereby a satisfactory operatingtemperature may be maintained in the trailing edge with reduced coolantrequirements.
 5. The improvement of claim 1 further characterized by andincluding a plurality of pin fins joining said sidewalls and extendingacross said trailing edge chambers.
 6. The improvement of claim 1wherein said airfoil is formed as a turbomachinery blade and includes anattachment portion and an airfoil portion intermediate and respectivelyadjacent inner and outer ends, said attachment portion adapted to securesaid airfoil to a rotor and formed with a chamber therein for receivingcoolant for delivery to said impingement means and said serpentinepassage chamber adjacent said trailing edge chamber.
 7. The improvementof claim 6 wherein said airfoil is formed with a necked openingintermediate said leasing edge chamber and said attachment portionchamber, said impingement means comprising a perforated tubular inserthaving an open inner end engaged in said necked opening and a closedouter end, and ports formed through said airfoil and communicating withsaid necked opening to facilitate forming and inspection of a brazedjoint between said insert and said airfoil.
 8. The improvement of claim6 wherein said longitudinal chambers are formed, in part, by a tip capclosing the outer end of said airfoil, said tip cap being perforated fordischarge of coolant from said longitudinal chambers.
 9. A fluid-cooledblade structure comprising a hollow cast member having airfoil andattachment portions intermediate open inner and outer radial ends, a tipcap secured to said cast member and closing said outer open end, saidairfoil portion defined by spaced leading and trailing edges joined byspaced concave and convex sidewalls, means formed internally of saidattachment portion for receiving a flow of coolant, a leading edgechamber formed internally of said airfoil portion adjacent said leadingedge, said leading edge chamber closed at its outer end by said tip cap,a thin-walled insert secured to said hollow cast member and projectinginto said leading edge chamber with its sidewalls in close spacedrelationship to the walls of said chamber, sAid insert disposed in flowcommunication with said coolant-receiving means, the walls of saidinsert being perforated so as to impinge coolant fluid from said insertchamber against said leading edge chamber wall, a trailing edge chamberformed internally of said airfoil portion adjacent said trailing edgeand closed at its outer end by said tip cap, a serpentine passage formedinternally of said airfoil portion, in cooperation with said tip cap,intermediate said leading and trailing edge chambers, with the portionof said serpentine passage adjacent said trailing edge chamber in flowcommunication with said coolant-receiving means, a plurality ofpassageways extending between said trailing edge chamber and saidadjacent serpentine passage portion for delivery of said coolant to saidtrailing edge chamber, said tip cap being perforated so as to permitefflux of said coolant from said chambers and said serpentine passagethrough the outer end of said blade structure, a plurality offilm-cooling passages formed through at least one said sidewall fordelivery of a film of coolant thereto from said leading edge chamber,and a plurality of passageways formed through said trailing edge forefflux of said coolant from said trailing edge chamber.
 10. Thefluid-cooled blade structure of claim 3 further characterized by andincluding a plurality of ribs projecting into said serpentine passagefrom said sidewalls, with the ratio of rib projecting height to thespacing of said sidewalls being at least about 0.02.
 11. Thefluid-cooled blade structure of claim 9 further characterized in thatsaid trailing edge passageways are inclined relative to the chordwiseaxis of said airfoil portion.